Polymerization inhibitor



Un t d S es. i te POLYMERIZATION INHIBITOR David W. McDonald, Texas City, Tex., assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Filed May 8, 1958, Ser. No. 733,830 8 Claims. (Cl. 252-1) This invention relates to the inhibition of polymerization. In one embodiment, it pertains to the inhibition of undesirable polymer growth in processing equipment. Specifically, it is concerned with a method for the stabilization of diacetylene or of mixtures containing diacetylene against polymerization and the stabilized compositions so produced.

If acetylene is produced from hydrocarbons, e.g., by the well known electric arc process or by thermal decomposition or dissociation, the acetylene-containing gas mixture produced generally contains diacetylene as well, in amounts ranging from as little as 0.05% to as much as 5%. The purification of such an acetylenic gas mixture is usually accomplished by the selective action of suitable a I solvents. A great number and varietyof solvents have been proposed and are effectively employed in well-developed purification processes. However, in these conventional methods of absorption and stripping, the gas mixture is exposed to conditions of temperature and pressure under which some of the diacetylene present polymerizes, and provision must be made in all such processes for periodic removal of the diacetylene polymers to prevent their excessive build-up in the solvent in the absorption step. This requires add.tiona1, specialized filtration equipment as well as added process steps which are costly with regard to both time and capital expense. Frequently, too, the diacetylene polymer collects in the less accessible parts of the system, fouling up equipment lines, columns, and the like. Usually, this particular polymer is of such a small particle size that it plugs the filter used for separating it, so that only a small amount can be filtered in each operation and an inordinate length of time is required to wring the filter cake dry.

Methods have been proposed for removal of diacetylene from the gas stream, but these are cumbersome and expensive since they require additional process steps prior to the usual solvent purification operation which utilizes special equipment and significant quantities of special chemicals for treating purposes.

It is an object of the present invention, therefore, to provide a method whereby undesirable polymer growth in the solvent purification of acetylene is inhibited.

It is a further object of the invention to provide a method for stabilization of diacetylene against polymerization.

It is a still further object of the invention to provide novel stabilized compositions comprising diacetylene, a solvent therefor, and an added polymerization inhibitor which do not polymerize when subjected to conditions under which such compositions lacking the inhibitor polymerize readily and rapidly.

Other objects and advantages of the invention will be apparent from the following description and the appended claims.

According to the invention, diacetylene contained in a solvent is stabilized against polymerization by the addition thereto of small quantities of 2-vinyl pyridine. The compositions comprising diacetylene, a solvent therefor, and a minor amount of 2-vinyl pyridine will not exhibit any significant polymer formation on storage or when subjected to the temperatures ordinarily encountered in solvent purification systems for acetylene purification.

The following examples illustrate the invention but are not to be construed as limiting it in any manner.

EXAMPLE 1 Diacetylene was generated by dropping 40% sodium hydroxide into a well-stirred solution of l,4dichlorobutyne in ethanol at a temperature of approximately C. The product gas was passed through Dry Ice traps and then allowed to bubble through a fritted gas bubbler into technical-grade butyrolactone at room temperature to make a stock solution of 0.3 g. of diacetylene per milliliter of solution. In the polymerization tests, 20 ml. of a test mixture containing a known amount of the diacetylene stock solution, butyrolactone, water, and a weighed amount of the 2-vinyl pyridine inhibitor were introduced into a thick-walled test tube. The mixture was frozen and the end of the test tube was drawn off in a torch flame to make a sealed ampule.- The sealed ampules were wrapped in bronze screen and placed in an oven maintained at C. for 16 hours, after which they were removed and inspected for polymer content. Blanks were run in which only butyrolactone and mixtures of butyrolactone,--water' and-diacetylene were present. Results .of a series of such tests are presented in Table I. All proportions given are-on a weight basis with the amounts of diacetylene and inhibitor being expressed as percent by weight of the total composition.

Table I Test Mixture Condition of Test Mixture 1:1 BL -HzO 1:1 EL -H1O plus 1% 2-vinyl idl e Dy H 1:1 Bil -.120 plus 0.25% d1- acetylene.

4 Same as in Test No. 3 plus Dark,red-v1ue colored solution 0.01% 2-viu' l pyridine. no visi'ole put. 5 Same as in Test No. 3 plus Slme as in Test N0. 4 above 0.1% 2-vinyl pyridine. exizept somewhat darker co or. 6 Same as in Test No. 3 plus Same as in Test No. 4 above.

1.0% 2-viuv1 pyridine. 7 1:1 Bil -J20 plus 0.5% di- Heavy brown ppt. settled in acetylene. bottom of tube; liq id also i 11 of suspended polymer. 8 Same as in Test No. 7 pl 1s Dark, murky, brownish-red 0.01% 2 vinyl pyridine. wine sol'tion; no visible ppt. but a small dark ring on wall at liquid-vapor interface. 9 Same as in Test No. 7 plus Clear, deep red wine solution;

0.1% 2-vinvl pyridine. no visiale solids. 10 Same as in Test No. 7 plus Same as in Test No. 9 above.

0.5% 2-vinyl pyridine.

l Butyrolactone.

EXAMPLE 2 A series of polymerization tests were conducted in the same manner as those in Example 1 except that acetylene solvents other than butyrolactone were employed. In each series, the stock solution of diacetylene was made up by bubbling the diacetylene into the solvent being used as the testing medium or environment. For each series, blanks were run consisting of solvent-water mixtures, solvent-water-diacetylene mixtures, and solvent-water-inhibitor mixtures. Results of these tests are presented in Table H.

Table II Test N 0. Test Mixture Condition of Test Mixture AI 1:1 DMF -HzO Clear, Watcr-wlite solrticn. A-II-. 1:1 DMF H2O plus 0.25% Clerr yellovlish srpernetant diacetylene. liqi id, extrenrly heavy V brown coagulated: preripitate. A1 1:1 DMF-H2O plus 0.5% Clear, light yellow solution.

2-vlnyl. pyridine. A-2 Sa-Ire as A-II above plus Fairly clear, yollow-broun 0.01% 2-vinyl pyridine. s1 pernatznt liqt id; rrcdi m an 01 nt h'onn coagilaicd ppt.; light film" on t1 be walls. A3 Sarre as A-II above plus Fairly leavy dark brovn S1 s- 0.1% 2-vinyl pyridine, pension; snall a-rrornt finely divided ppt; heavy film on liqi iii-surface. A-4. Same, asv i-II above plus Clear enter sol iion, no 0.5%2-v1nyl pyridine. visible ppt.; slight film on liq= id s rface. CI 1:1 Acetonyl acetoneHz-. Clear, ntcdit m-yellow solution. O-IL... 1:1 Acetonyl, acetoneI-lz0 Light brown suspension;

plus 0.25% diacetylcne. finely-divided broun preciritate. C1 1:1 Kcetonyl acetone-H1O Clear, pale amber solution;

pli.s0.% 2-v1nyl pyridine. no pretipitate. C-2. Sane as C-II above plus -Cle ar,IIcdiI in amber solution;

0.01% 2-vmyl pyridine. no preciritate. C-3 Sane as C-II above plus Same as O-2 above.

0.1% 2-viny1 pyridine. C4-.-. Sane as C-II above plus Same as (3-3 above except 0.5% 2- vinyl pyridine. dark amber in color. D-I' 1':1 1,4-Dl0xa11-Hz0 Perfectly clear, water-white S011 tion. DIl- 1:1 DioxaneH 0 p1us0.25% Extremely heavy, coagrlated diacetylene. red-brown prtciritate; clear amber srpernat: nt liqiid. 1:1 D onne-H10 plus'0.5% Clear, yellow solution.

2 vinyl'pyridine. Saneas D-II abovaplus Brown suspension with very 0.01% avinylpyridina. sn all, zmoi nt of ac'tt al precipitate; trace of flaky brown ppt. on surface cf liqr id; 13-3.--" Same as I )-II- above plus Mediin-dark, red-nine solu- O;1% 2-v1nyl" pyridine. lion; no visible pretipitate. 10-4... Same as, D-II. above plus same'asD iyabovel 0.5% 2-vinylpyridir.e.

1 Dimethylformamide.

From the results of' these qualitative tests, it-will" be seen that inhibition of polymerization of diacetylene can be effected with as little as 0.01% of2-vinyl pyridine. While the preceding examples have illustrated specific embodiments of the invention, substantial variation may be made without departing from the scope thereof. For example, the quantity of 2-vinyl pyridine used to inhibit the polymerization of diacetylene can be varied widely, the amount used being determined upon the basis of the amount of diacetylcnc, present and the degreeof inhibition desired. In general, only minor quantities-of inhibitor; are required. Concentrations of 2-vinyl pyridine in the range of about 0.01% to about by weight of'the total composition containing diacetylene are suitable, with concentrations from about 0.1% to about 1% being preferrcd. The stabilizing agent may, of course, be employed in as great a concentration as desired.

The inhibitor of the invention is not restricted to use with the solvents as set out in the examples above. 2-vinyl pyridine may be used to inhibit the polymerization of diacetylene in other like organic solvents commonly employed in the purification of acetylene by absorption techniqucs. In solvent systems where such solvents are used to absorb acetylene from a gas stream containing it in combination with other gases including diacetylene, polymerization of the diacetylene is effectively inhibited by the presence of a minor amount of 2-viny1 pyridine. To inhibit polymer formation during the absorption-stripping operation, the inhibitor can be added directly to the solvent fecdstream, or it may be introduced as'a solution of the desired concentration at some point in-the absorption A, system. The inhibiting power of the 2-vinyl pyridine is not affected by continual reuse; hence, recirculation of the solvent provides as efiective inhibition as the introduction of the fresh solution.

The inhibitor of the invention may also be utilized for preparing stabilized compositions of diacetylene in a solvent which can be safely stored over a period of time without undergoing polymerization with its usual attendant hazards.

This application is a continuation-in-part of my copending application Serial No. 391,747, filed November 12, 1953, now abandoned.

What is claimed-is:

1 A- composition of matter consistingessentially of diacetylcne, a solvent therefor chosen from the group consisting of butyrolactone, dimcthylformarnide, acetonyl acetone and 1,4-dioxanc, and 2-vinyl pyridine, said composition containing diacetylene in concentrations up to about 0.5% by weight and 2-vinyl pyridine in an amount from about 0.01% to about 5% by weight of the total composition.

2 A composition ofmatterconsisting essentially of diacetylcnc, a solventtherefor chosen from the group consisting of butyrolactone, dimethylformamide, acetonyl acetone and 1,4-dioxanc, and 2-vinyl pyridine, said composition containing diacetylene in concentrations up to about 0.5 by weight and 2-vinyl pyridine in an amountfrom. about 0.1% to about 1% by weight of the total composition.

3. Acomposition of matter consisting essentially of di-- acetylene, butyrolactone,and:2-vinyl pyridine, said composition containing diacetylene in concentrations up to abo ut.0 .5.7:v by weight and. 2-viny1 pyridine in an amount from: about. 0.01% to aboutv 5%v by wcightof the total composition. V

4. Acornposition. of. matter consistingessentiallyof die acetylene, butyrolactone, and 2-vinyl pyridine, said com position containing diacetylene in concentrations. up to about.0.5 by weight and 2-vinyl pyridine in an amount from about 0.1% to. about 1% by weight of the total composition.

5.. A composition. of matter consisting essentially of diacctylcnc, dimethylformamidc, and 2-vinyl pyridine, said composition. containing diacetylene in concentrations up to: about. 0.5% by weight and 2-vinyl pyridine in an amountfrom about.0,l%. to about 1% by weight of the totalcomposition.

61'. Acomposition of. matter consisting essentially of diacetyl'enc, acetonyl acetone, and 2-vinyl pyridine, said composition containing diacctylene. in concentrations up to; about 0.5%: by weight and 2-vinyl pyridine in an amount from'about 0.01% to about 5% by weighttof the total composition.

7. A composition of matter consisting essentially of diacetylcne, acetonyl acetone, and 2-vinyl pyridine, said composition containing diacetylene in concentrations up to aboutv 0.5% by weight and 2-vinyl pyridine in an amount from'about 0.1% to about 1% byweight of the total composition.

8.. A composition of matter consisting, essentially-of diacetylenm. 1,4 -dioxane,, and 2-vinyl pyridine, said composition containing diacetylene in concentrations up to aboutv 0.5 by weight and 2-vinyl pyridine in, an amount from aboutv 0.1% to. about 1% by weight ofthe-total composition.

References. Cited inthc file of this patent UNITED STATES PATENTS 

1. A COMPOSITION OF MATTER CONSISTING ESSENTIALLY OF DIACETYLENE, A SOLVENT THEREFOR CHOSEN FROM THE GROUP CONSISTING OF BUTYROLACTONE, DIMETHYLFORMAMIDE, ACETONYL ACETONE AND 1,4-DIOXANE, AND 2-VINYL PYRIDINE, SAID COMPOSITION CONTAINING DIACETYLENE IN CONCENTRATIONS UP TO ABOUT 0.5% BY WEIGHT AND 2-VINYL PYRIDINE IN AN AMOUNT FROM ABOUT 0.01% TO ABOUT 5% BY WEIGHT OF THE TOTAL COMPOSITION. 